Study On Preparation Of Silica From Diamond Wire Cutting Waste Of Crystalline Silicon

With the increasing application of solar cells,the demand for crystalline silicon wafers as its basic components has also increased significantly.Generally,diamond-wire cut crystalline silicon rods are used to produce crystalline silicon wafers.In the process,there will be nearly 40%of solar-grade silicon is ground into diamond-wire cutting waste of crystalline silicon.Because there is no reasonable recycling method,the waste of material is generally piled up,which not only pollutes the environment but also wastes resources.In recent years,many studies have used new raw materials to prepare silica,but most of them require pretreatment such as impurity removal,increase the production process,with negative effect of the quality of silica products.Due to the high purity of crystalline silicon diamond wire cutting waste,the reaction can be performed without pretreatment such as impurity removal,and the particle size is small,so the reaction activity is high.The preparation of silica can not only solve the environmental problems and the waste of resources caused by crystalline silicon cutting waste,and it can provide new ideas for the production of silica.The physical and chemical properties of the crystalline silicon cutting waste are analyzed,and the crystalline silicon cutting waste is obtained:the particle size is very fine,which average particle size is 1.174 μm;the main component is Si,with a content of 84 wt%,followed by SiO₂,with a content of 13.5 wt%;the shape is thin and chipped and is caused by grinding.The influence of three key factors,concentration of sodium hydroxide solution,reaction temperature and reaction time,on the preparation of intermediate from crystalline silicon cutting waste was determined by single factor experiment.The influence level of the three key factors to crystalline silicon cutting waste has been quantified by BBD response surface optimization.And find the optimal process conditions.The sequence of influence of the three factors on the reaction rate under conventional reaction condition is the reaction temperature>NaOH concentration>reaction time,and the optimal process factors are NaOH concentration of 1.58 mol/L,reaction temperature 88.38℃,reaction time 3.22 h,the reaction rate is 99.7%;the sequence of influence of the three factors on the reaction rate under magnetic stirring condition is NaOH concentration>reaction temperature>reaction time,and the optimal process factors are NaOH concentration of 1.41 mol/L,reaction temperature of 87.16℃,and reaction time of 1.77 h,the reaction rate is 99.8%.The single factor experiment has been used to find the influence of three key factors:reaction temperature,endpoint pH,and hydrochloric acid concentration on the production of silica.The optimal process conditions for the production of intermediate to silica are 70℃,pH 7 and hydrochloric acid concentration 15 wt%,which silica has a maximum DBP of 2.73 mL/g and a maximum BET of 326.3 m²/g.The silica test results which according to national standards showed that the silica was amorphous and had an average particle size of 20～30 nm.Each test item met or even surpassed the national standard.The effect of n-butanol dosage on the modification of silica has been determined by single factor test.According to the oil absorption value and FTIR analysis results,the optimal n-butanol dosage of modified silica is 0.6 mL.